Absorption-type refrigeration systems have been used for many years in the residential and commercial air conditioning and refrigeration markets. Compressor-type refrigeration systems have been used even more extensively in these markets for the same purposes.
In prior art absorption-type systems low-pressure refrigerant in its vapor state is absorbed by an absorbent liquid in an absorber, the absorber being cooled by water or air. The resulting refrigerant/absorbent solution is pumped to a higher pressure and supplied to a separator unit which utilizes heat (high temperature boils off the refrigerant) or very high pressure (osmotic membrane passes only the refrigerant) to separate the refrigerant from the absorbent. The separated refrigerant is then condensed, expanded to a low pressure (resulting in a low temperature) and delivered to an evaporator which extracts heat from the space being refrigerated.
Conventional ammonia absorption refrigeration systems utilizing ammonia, for example, as a refrigerant, and water as the absorbent liquid, and heat for the separation process, are capable of achieving low temperatures less than 32.degree. F. and even down to -25.degree. F. or lower. However, the ratio of refrigeration provided to the energy required by such a cycle, called the coefficient of performance ("COP"), is typically significantly less than 0.50.
Osmotic-membrane-absorption refrigeration cycles are also capable of reaching low temperatures and may have a COP higher than conventional ammonia/water heat-separation systems, but require very high pressures, of the order of 2,000 psia or more to force the refrigerant through the pores of the osmotic membrane. Such high pressure must be handled with considerable care and even then may create a potentially hazardous environment.
Conventional compressor-type systems rely on electricity as the power source. Although this type system is more efficient than heat-separation-absorption-type systems, i.e., providing a COP of around 4, the electricity to run such systems is approximately ten times more costly than the gas for heat-separation absorption type system. The cost savings of gas vs. electricity is not present in an osmotic-membrane-separation system when the high pressure pump is driven by an electric motor. In addition, compressor-type pumps, the refrigerants, for compression-type systems, may be very destructive of the ozone layer.
There is a need in the refrigeration field for an energy efficient system that does not require high working pressures or utilize a working fluid that is destructive of the ozone layer.